Pentaﬂuoropyridine as a ﬂuorinating reagent for preparing a hydrocarbon soluble b -diketiminatolead( II ) monoﬂuoride w z

A well-designed method for the preparation of a b -diketiminato lead( II ) monoﬂuoride has been developed using LPbNMe 2 (L = [CH{C(Me)(2,6-i Pr 2 C 6 H 3 N)} 2 ]) and pentaﬂuoropyridine (C 5 F 5 N). The resulting LPbF was used for the synthesis of amidinatosilicon( II ) monoﬂuoride. Moreover the activation of a ketone was observed when the LPbF was treated with PhCOCF 3 .

Organometallic fluorides of group 14 elements are important due to their application in synthetic methodology as well in the laboratory as in industry. 1In the literature, the known group 14 fluoro compounds are preferentially in the +4 oxidation state. 2 Only few examples of organogermanium(II) and tin(II) monofluorides are known. 3,4In contrast, the chemistry of Pb(II) tends to be dominated by compounds with inorganic ligands.Organometallic compounds with two valent lead are relatively rare and their chemistry is poorly explored. 5,6ecently, we reported on a variety of lead complexes which can be used as precursors for new lead derivatives. 7However a fluoride derivate of lead like its lighter congener is still elusive.The difficulties with lead-based chemistry are its tendency to form insoluble precipitates besides its susceptibility to undergo redox chemistry to form metallic lead.We anticipated that the introduction of sufficiently large substituents is necessary for kinetic stabilization of such reactive species.Such a complex even as a monomer can be obtained by exploiting the unique property of the b-diketiminate ligand L (L = [CH{C(Me) (2,6-iPr 2 C 6 H 3 N)} 2 ] that coordinates tightly to the lead atom, and is also capable of providing enough steric bulk to prevent the formation of oligomers.Moreover, the Pb-F bond strength is the weakest within the element(II) fluorides of group 14, due to the large Pb 2+ radius.However at the same time relatively little is known about silicon(II) monofluorides compared with other silicon halides, probably due to the lack of convenient synthetic routes to the fluoro compounds. 8This encouraged us to synthesize lead (II) and silicon (II) monofluoride.Herein we report on the synthesis of hydrocarbon soluble b-diketiminatolead(II) and amidinatosilicon(II) monofluorides and the reactivity of the former with 2,2,2trifluoro acetophenone.
For the preparation of silicon(II) and lead(II) monofluorides initially we followed the routes which are already applied for the synthesis of germanium(II) and tin(II) monofluorides.3b,4b However we were not able to obtain the expected product following this protocol.Recently, we reported on the synthesis of lead(II) amide, 7c e.g.LPbNMe 2 (1) and its reaction with ketones, where the dimethylamino group acts as a nucleophile.7c Moreover, we demonstrated that the para fluorine atom of the pentafluoropyridine is easily activated by silylenes. 9onsequently, we treated LPbNMe Compound 2 is a yellow solid soluble in benzene, THF, and toluene.It shows no decomposition on exposure to dry air. 2 was characterized by 1 H, 13 C, 19 F, and 207 Pb NMR spectroscopy, EI mass spectrometry, elemental analysis, and X-ray structural analysis.We recorded the low temperature (À80 1C) 19 F and 207 Pb NMR sprectra.The 19 F NMR spectrum of 2 exhibits a resonance at d À102.7 ppm, which is accompanied Institut fu¨r Anorganische Chemie, Universita¨t Go¨ttingen, Tammannstrasse 4, 37077 Go¨ttingen, Germany.E-mail: hroesky@gwdg.de,dstalke@chemie.uni-goettingen.de;Fax: +49 551-39-3373 w Electronic supplementary information (ESI) available: Synthetic and spectral details.CCDC 808034 ( 2) and 808035 (6).For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c1cc11310k z Dedicated to Professor Reinhart Ahlrichs on the occasion of his 70th birthday.
by two 207 Pb satellites (d À106.4 and À99.0 ppm).The 207 Pb NMR spectrum shows a doublet at d 787.4 ppm, with a coupling constant of J( 19 F-207 Pb) = 2792 Hz, which is upfield shifted when compared with that of 1 (d 1674 ppm).7c The satellite resonances and coupling constants of the 19 F and 207 Pb NMR spectra are not observed, when the measurements are carried out at room temperature.This suggests that the Pb-F bond is kinetically labile on the NMR time scale at room temperature.Dissolving 2 in hot n-hexane and keeping it for two days at À32 1C resulted in yellow single crystals suitable for X-ray structural analysis.w 2 crystallizes in the monoclinic space group P2 1 /n, with one molecule in the asymmetric unit (Fig. 1).yCompound 2 exists as a monomer in the solid state with a terminal bound fluorine atom, which has the potential to be used as a fluorinating agent.The coordination polyhedron around the lead atom comprises two nitrogen atoms from the supporting ligand, one fluorine atom, and one lone pair featuring a distorted tetrahedral geometry.The Pb-F bond length is 2.088(17) A ˚, obviously longer when compared with those of Ge-F (1.805(17)A ˚) in LGeF 3b and Sn-F (1.988(2)A ˚) in LSnF.4b The average Pb-N bond lengths are 2.317(36) and 2.296(34) A ˚, and slightly longer than the Pb-N bond lengths in 1 (2.155(10)A ˚).
After the isolation of lead(II) monofluoride, we focused on the synthesis of silicon(II) monofluoride.The stable LPbF contains a terminal fluorine atom, which can serve as a nucleophilic reagent.However, the reaction of silicon(II) chloride L 1 SiCl [L 1 = PhC(NtBu) 2 ] 11 with Me 3 SnF, LGeF, LSnF, and LPbF, respectively, as a fluorinating reagent mostly resulted in the formation of L 1 SiF 3 12 and some unidentified products.Finally we used L 1 SiCl(BH 3 ) (4) 13 instead of L 1 SiCl, and treated this compound with LPbF.
The 1 : 1 reaction of L 1 SiCl(BH 3 ) with LPbF in toluene at À30 1C leads to the formation of L 1 SiF(BH 3 ) (5) and LPbCl (Scheme 2).Compound 5 is a white solid soluble in benzene, toluene, and THF and shows no decomposition on exposure to dry air.It was characterized by 1 H, 11 B, 13  Here it is worth mentioning that Jutzi et al. reported the formation of unstable Cp*SiF (where Cp* indicates 1,2,3,4,5pentamethylcyclopentadienyl), which is highly reactive and dimerizes to the unstable disilene Cp*(F)SiQSi(F)Cp*, which further reacts to the isolable cyclotetrasilane by a [2 + 2] cycloaddition. 14fter the successful reaction of 2 with 4, we turned our attention to the activated ketone, 2,2,2-trifluoro-acetophenone.This reaction is quite different when compared with those of LGeH or LSnH and PhCOCF 3 . 15In the latter case the nucleophilic addition reactions occurred under formation of germanium(II) or tin(II) alkoxide, respectively.
Single crystals suitable for X-ray structural analysisw were obtained when a concentrated solution of 6 in a mixture of THF and n-pentane was stored at À5 1C.6 crystallizes in the monoclinic space group P2 1 /c with one molecule in the asymmetric unit.yThe structure of 6 (Fig. 2) reveals the homoleptic nature of the complex and contains two six-membered OC 3 NPb rings, that are connected by the common lead atom.Thus, the Pb atom is four-coordinate and adopts a distorted trigonal bipyramidal geometry with two nitrogen atoms of the b-diketiminate ligand occupying the axial positions, two oxygen atoms, and the lone pair residing in the equatorial positions.As expected, the average Pb-N (2.620 av A ˚) bond length is longer than those of the corresponding bonds in 2 (2.307 av A ˚).The average Pb-O bond distance (2.169 av A ˚) is longer than that in LPbOiPr (2.135(3)A ˚) and LPbOtBu (2.126(3)A ˚).This journal is c The Royal Society of Chemistry 2011 6 has been also characterized by spectroscopic and analytic measurements in addition to the X-ray structural analysis.The 1 H NMR spectrum of 6 agrees with the solid state structure.Two singlet resonances were observed for the methyl (d 2.96 and d 1.86 ppm) and the CH protons also appear as another singlet at d 5.19 ppm.In the 19 F NMR spectrum of 6 the C-F resonance appears as a sharp singlet at d À76.2 ppm.This shows an upfield shift compared to that of the ketone, PhCOCF 3 (d À71.6).The 207 Pb NMR spectrum of 6 exhibits a singlet which is shifted downfield (d 853.9 ppm), when compared with 2 (d 787.4 ppm).Compound 6 is found to be sensitive towards moisture and air and it is soluble in benzene, THF, toluene, and diethyl ether.
In conclusion, after the successful syntheses of amidinatosilicon(II) and b-diketiminatolead(II) monofluorides, the series of fluorides with the heavier low valent group 14 elements has been completed, although the corresponding stable fluoride of low valent carbon remains still elusive.The reaction of lead(II) monofluoride with PhCOCF 3 results in a homoleptic lead compound in which the ketone is incorporated.Currently we are investigating the reactivity of this lead(II) monofluoride as fluorinating reagent.
Support of the Deutsche Forschungsgemeinschaft and the DNRF funded Center of Materials Crystallography is highly acknowledged.

Notes and references
2 (1) in a 1 : 1 ratio with pentafluoropyridine (C 5 F 5 N) in diethyl ether or THF at room temperature (Scheme 1).After 12 hours it resulted in the formation of the b-diketiminatolead(II) monofluoride, LPbF (2) together with 4-dimethylaminotetrafluoropyridine (4-NMe 2 C 5 F 4 N) (3).The 1 H NMR spectrum of the crude reaction mixture indicates the complete disappearance of the resonances for NMe 2 (d 3.80 ppm) of 1, and the formation of a new signal at d 2.60 ppm for 3.This reaction is comparable with the synthesis of 4-dimethylaminotetrafluoro-pyridine (3) from dimethyl amine or trimethylsilyl-dimethylamine (Me 3 SiNMe 2 ) and C 5 F 5 N. 10 The energy required to cleave the C-F bond is compensated by the formation of a C-N bond.
C, 19 F, and 29 Si NMR spectroscopy, EI mass spectrometry, and elemental analysis.The resonance corresponding to the tert-butyl protons appears as a singlet (d 1.0 ppm) in the 1 H NMR spectrum.The 19 F NMR spectrum of the reaction mixture exhibits the consumption of lead(II) monofluoride and indicates the formation of a new 19 F resonance at d À121.59 ppm, which is accompanied by 29 Si satellite signals (J = 438.17Hz).The 29 Si NMR spectrum shows a doublet of quartets (d 23.63 ppm and J( 29 Si-11 B) = 66.78 Hz) indicative for one silicon-boron and silicon-fluorine bond.The 11 B NMR spectrum is also consistent with the presence of one BH 3 group.No molecular ion peak was found in the EI mass spectrum of 5, but the most intense peak corresponds to [M + -BH 3 ].Therefore we conclude the preparation of silicon(II) monofluoride, L 1 SiF(BH 3 ) (5), was successful.